As a Roman Catholic, I'm not supposed to get offended with such a question.
Fortunately, more and more Protestants are realizing that they are not the only Christians. Christianity has tree main branches, Roman Catholic, Eastern Orthodox and Protestant.
I hear this up north also, mostly when I visit southern PA and parts of Ohio where I have relatives. And I have been told by well meaning folks when I ascertain that I am Catholic, that I am not Christian AT ALL. I don't get offended anymore. And as a once hopeful adoptive parent, I was brushed off and turned down flat from a Christian agency when I responded to their question about religion. The only turn down.
Christianity has many branches ~ Catholicism, Reform, Evangelical, Apostolic, Mennonite, Amish, Cather, Arian, 4 Square Gospel, and so forth.
Lots of ignorance there, apparently.
Here is the big test... which "branch" was founded by Jesus Christ?
And which two branches come from the other? :^)
And here in the Northeast, it's not uncommon to hear someone ask, "Are you a Catholic?" when they really mean "Are you a Christian?" because Catholics are so dominant in some areas and let's just say that my mother is not burried in a Catholic cemetary because my father wouldn't agree to raise me Catholic, her father is burried in a steel vault in a Catholic cemetary because he converted on his deathbed from being a Lutheran, and my paternal grandmother's parents were burried in seperate cemetaries after being married for over 50 years because one was Catholic and the other was Protestant. I'm not trying to bash Catholics here but I'm simply trying to point out that Catholics aren't any more open-minded about Protestants when they are in the driver's seat. I think it's silly either way.